Transcript
Linux Audio for Smartphones System integration basics
1
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Overview
• • • •
• • •
2
Android audio stack overview Modern smartphone audio subsystems Traditional solutions ASoC – the Linux solution
• •
Design overview Brief introduction to chip drivers
Walk through of system audio driver construction Debugging tips Future directions
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Android audio stack
Applications
MediaPlayer MediaRecorder
AudioFlinger
libaudio
3
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Modern smartphone audio subsystems
HDMI
CPU
Earpiece
Speaker
Headset
Dock
Mixing
DSP
Cellular modem
4
© 2011 Wolfson Microelectronics plc
Bluetooth
April 2011
www.wolfsonmicro.com
Flexibility and complexity
5
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Traditional driver model
Memory
6
© 2011 Wolfson Microelectronics plc
Processing
Analogue
April 2011
www.wolfsonmicro.com
Traditional driver model
•
• •
7
Monolithic driver for each card
• •
No structure for managing off-CPU hardware Very little reuse
Tight coupling between application and kernel code
• •
Per-use case register settings Detailed register level knowledge of components
Time consuming
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
The Linux solution
•
• • • • •
8
ASoC embedded audio framework
• •
Merged since 2.6.21, April 2007 Provides standard ALSA interface to applications
Reusable drivers for each chip Minimal per-system drivers Use case configuration done by userspace Automatic and transparent power management More reuse, less coupling
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Dynamic Audio Power Management
• • •
Looks for audio paths connecting inputs to outputs Powers only components in an active path Automatically activates DACs and ADCs DAC
Speaker Mixer
FM radio
9
© 2011 Wolfson Microelectronics plc
Headset
April 2011
www.wolfsonmicro.com
ASoC CODEC drivers
•
•
10
Four classes of control
• • • •
Audio processing controls (eg, volume, effects) Audio routing controls (DAPM controls and routes) Power controls (DAPM widgets, bias) Stream control (Digital audio streaming)
Mostly direct mapping into register map •
SOC_DOUBLE_R_TLV("DAC1 Volume", WM8994_DAC1_LEFT_VOLUME, WM8994_DAC1_RIGHT_VOLUME, 1, 96, 0, digital_tlv),
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Driver integration walkthrough
“Baseband”
Headset
Speaker S3C6410/ WM0010
WM8915 CODEC Mics WM9081 Amplifier
Subwoofer
http://opensource.wolfsonmicro.com/content/speyside-audio
11
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Application layer
•
• •
12
AudioPolicyManager and AudioHardware
• •
platform/hardware/alsa_sound – Generic ALSA, asound.conf, LGPL devices/samsung/crespo – Nexus S, hard coded, Apache licensed
Getting use cases
• •
Devices specified when streams are opened setMode()
Applying use cases
• • • • •
Run external utilities Use asound.conf Call raw ALSA control APIs Apply settings with ALSA UCM Using common base use cases helps
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Debugging tips - DAPM
•
• • •
Data in debugfs
• •
CONFIG_DEBUG_FS mount –t debugfs /dev/null /debug
codec_reg – Register map dapm_pop_time – log sequences dapm directory SPKL: Off in 0 out 1 in "DAC2L" "DAC2L" out "static" "SPKL PGA"
•
13
Tools:
•
git://git.opensource.wolfsonmicro.com/asoc-tools.git
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Debugging tips - general
• • • • • • •
14
Audio stuck – check clocking Silent audio – check volumes and mutes Use bypass paths to bisect Turn volumes up to maximum Make sure machine drivers check error codes Check kernel logs for errors 2.6.38 and later support trace points • http://www.sirena.org.uk/log/2011/01/22/tracing-asoc-with-trace-points/
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
Future work
• • •
• • •
15
Nicer handling of digital basebands Resolve headset detection API compatibility Greater use of DSP
• •
Enhanced features – ambient noise cancellation, beam forming, offloaded decompression, speaker compensation Even more dynamic reconfiguration of the audio subsystem
Coefficient management and in-system calibration Use case development and management
• •
Media controller API User interfaces for configuration development
ASoC conference, 4th-5th May
•
http://www.slimlogic.co.uk/?p=268
© 2011 Wolfson Microelectronics plc
April 2011
www.wolfsonmicro.com
